Ideally, trimming capacitors and potentiometers should have multi-turn trimming capability, be sealed from ambience, and be inexpensive to manufacture. This combination of features, however, has yet to be achieved in the devices of the prior art.
Unsealed trimming capacitors and potentiometers may possess the multi-turn character by having an excentric gear arrangement that provides multi-turn trimming capabilities. They may also be made relatively inexpensive to manufacture by having one gear compactly located within the bounds of another gear which may be turned by simply rotating an externally accessible gear shaft. This open design however presents several problems, most being attributable to the fact that chemical solutions may form within the device through the ingress of various agents from ambience. These solutions tend to modify the operational characteristics of the dielectric. Such unsealed devices also tend not to meet stringent salt spray and humidity test specifications. Furthermore, costly production controls must normally be employed in producing the devices to prevent solvents and degreasers from damaging them during manufacture.
Sealed trimmers, of course, do exist but they usually are of the fractional-turn type and thus have poor resolution and are difficult to set accurately and to remain accurately set without drifting. Concentric ring trimmers, which do possess multi-turn capabilities, may be capped so as to be sealed. An example of such a sealed, multi-turn trimmer is the model 1102 trimming potentiometer manufactured by Murata Erie North America Inc. with a planetary gear drive. Again, it is relatively large and expensive to manufacture.
Thus, there remains a need to provide a multi-turn sealed trimmer, such as a trimming capacitor and a trimming potentiometer, which is relatively inexpensive to manufacture. It is the provision of such trimmers to which the present invention is therefore primarily directed.